Dependence Of Na Research Articles

Dependence of Na+ leakage on intrinsic properties of cation exchange resin in simulated secondary environment for nuclear power plants

Material corrosion in nuclear power plant (NPP) is not controlled only by amine injection but also by ion exchange (IX) which is the best option to remove trace Na+. This study was conducted to understand the Na+ leakage characteristics of IX beds packed with ethanolamine-form (ETAH-form) and hydrogen-form (H-form) resins in the simulated water-steam cycle in terms of intrinsic behaviors of four kinds of cation-exchange resins through ASTM test and Vanselow mass action modeling. Na+ was inappreciably escaped throughout the channel created in resin layer. Na+ leakage from IX bed was non-linearly raised because of its decreasing selectivity with increasing Na+ capture and with increasing the fraction of ETAH-form resin. Na+ did not reach the breakthrough earlier than ETAH+ and NH4+ due to the increased selectivity of Na + to the cation-exchange resin (H+ < ETAH+ < NH4+ ≪ Na+) at the feed composition. Na+ leakage from the resin bed filled with small particles was decreased due to the enhanced dynamic IX processes, regardless of its low selectivity. Thus, the particle size is a predominant factor among intrinsic properties of IX resin to reduce Na+ leakage from the condensate polishing plant (CPP) in NPPs.

Sugar, a powerful substitute for ethanol in ethanol postdependent rats: Relevance for clinical consideration?

Sugar has been shown to be a powerful substitute for drugs in preclinical studies on addiction. However, the link between sugar intake and alcohol use disorder (AUD) is poorly understood. We assessed the influence of sucrose on ethanol drinking in both nondependent (ND) and dependent (D) Long-Evans rats during acute withdrawal using the postdependent state model. Ethanol (10%-40%) and sucrose (1%-4%) solutions were offered in an operant paradigm either independently or concurrently under ratio schedules of reinforcement. We showed that D rats displayed an enhanced motivation for both 10% ethanol solution (10E) and 4% sucrose solution (4S) as compared with ND rats, and a clear preference for 4S was observed in both groups. During acute withdrawal, D rats showed a strong motivation for 30% ethanol (30E), even when adulterated with quinine, but still preferred 4S despite the fact that a high level of negative reinforcement could be expected. However, when a premix solution (30E4S) was offered concurrently with 4S, the preference for 4S was lost in D animals, which consumed as much premix as 4S, whereas ND animals displayed preference for 4S. Altogether, those results suggest that reinforcing properties of sucrose surpass those of ethanol in D rats under acute withdrawal, which indicates that sugar is a powerful substitute for ethanol. Our results suggest that craving for sugar may be increased in AUD patients during withdrawal and raise the issue of dependence transfer from alcohol to sugar.

The cardiac Na+/K+ ATPase: An updated, thermodynamically consistent model

The Na+/K+ATPase is an essential component of cardiac electrophysiology, maintaining physiological Na+ and K+ concentrations over successive heart beats. Terkildsen et al. (2007) developed a model of the ventricular myocyte Na+/K+ ATPase to study extracellular potassium accumulation during ischaemia, demonstrating the ability to recapitulate a wide range of experimental data, but unfortunately there was no archived code associated with the original manuscript. Here we detail an updated version of the model and provide CellML and MATLAB code to ensure reproducibility and reusability. We note some errors within the original formulation which have been corrected to ensure that the model is thermodynamically consistent, and although this required some reparameterisation, the resulting model still provides a good fit to experimental measurements that demonstrate the dependence of Na+/K+ ATPase pumping rate upon membrane voltage and metabolite concentrations. To demonstrate thermodynamic consistency we also developed a bond graph version of the model. We hope that these models will be useful for community efforts to assemble a whole-cell cardiomyocyte model which facilitates the investigation of cellular energetics.

Usability of the lateral decubitus position on four-dimensional ultra-low-dose computed tomography for the detection of localized pleural adhesion in the pulmonary apical region.

Localized pleural adhesion (LPA) evaluation in the apical region is difficult even with four-dimensional ultra-low-dose computed tomography (4D-ULDCT) in the supine position due to smaller pleural movements. To assess usability of 4D-ULDCT in the lateral decubitus (LD) position for LPA detection in the apical region. Forty-seven patients underwent 4D-ULDCT of a single respiration cycle with 16-cm coverage of body axis in supine and LD positions with the affected lung uppermost. Intraoperative thoracoscopic findings confirmed LPA presence. A pleural point and a corresponding point on costal outer edge were placed in identical axial planes at end-inspiration. Pleuro-chest wall distance between two points (PCD) was calculated at each respiratory phase. In the affected lung, average change in amount of PCD (PCDACA) was compared between patients with and without LPA in total and two sub-groups (non-COPD and COPD, non-emphysematous and emphysematous patients) in supine and non-dependent (ND) LD positions. Receiver operating characteristic (ROC) curve analysis was performed to determine optimal thresholds in PCDACA for differentiating patients with LPA from those without. In COPD/emphysematous patients and total population, PCDACA with LPA was smaller than in those without in the supine and NDLD positions for overall, lateral, and dorsal regions. For the lateral region in COPD patients, area under ROC curve (AUC) increased from supine (0.64) to NDLD position (0.81). For the dorsal region in emphysematous patients, AUC increased from supine (0.76) to NDLD position (0.96). 4D-ULDCT in LD position may be useful for LPA detection in apical regions for COPD and/or emphysematous patients.

Energy conservation involving 2 respiratory circuits

Chemiosmosis and substrate-level phosphorylation are the 2 mechanisms employed to form the biological energy currency adenosine triphosphate (ATP). During chemiosmosis, a transmembrane electrochemical ion gradient is harnessed by a rotary ATP synthase to phosphorylate adenosine diphosphate to ATP. In microorganisms, this ion gradient is usually composed of [Formula: see text], but it can also be composed of Na+ Here, we show that the strictly anaerobic rumen bacterium Pseudobutyrivibrio ruminis possesses 2 ATP synthases and 2 distinct respiratory enzymes, the ferredoxin:[Formula: see text] oxidoreductase (Rnf complex) and the energy-converting hydrogenase (Ech complex). In silico analyses revealed that 1 ATP synthase is [Formula: see text]-dependent and the other Na+-dependent, which was validated by biochemical analyses. Rnf and Ech activity was also biochemically identified and investigated in membranes of P. ruminis Furthermore, the physiology of the rumen bacterium and the role of the energy-conserving systems was investigated in dependence of 2 different catabolic pathways (the Embden-Meyerhof-Parnas or the pentose-phosphate pathway) and in dependence of Na+ availability. Growth of P. ruminis was greatly stimulated by Na+, and a combination of physiological, biochemical, and transcriptional analyses revealed the role of the energy conserving systems in P. ruminis under different metabolic scenarios. These data demonstrate the use of a 2-component ion circuit for [Formula: see text] bioenergetics and a 2nd 2-component ion circuit for Na+ bioenergetics in a strictly anaerobic rumen bacterium. In silico analyses infer that these 2 circuits are prevalent in a number of other strictly anaerobic microorganisms.

Effects of different sleeping positions on intraocular pressure in secondary open-angle glaucoma and glaucoma suspect patients.

PurposeThe aim of this study was to investigate the effects of different recumbent sleeping positions of the head and body on intraocular pressure (IOP) in secondary open-angle glaucoma and glaucoma suspect patients, specifically pigmentary dispersion (PD) as measured using the ICare rebound tonometer.Patients and methodsA total of 44 eyes of 24 patients with PD were selected in this study. The IOP of 44 eyes was measured in the initial seated position, in the 4 recumbent positions, and again in the sitting position between each of the recumbent positions.ResultsThe IOP of the right eyes and left eyes was higher in each of the 4 recumbent positions compared to its initial sitting position (all P<0.001). Dependent (D) vs nondependent (ND) comparisons failed to show a significant difference. All lateral vs prone comparisons showed a higher average IOP in the prone position than in the lateral position regardless of D vs ND status. The range of recumbent IOP changes was −4 to +17 mmHg or −17% to +142%. A total of 64% had at least a ≥33% IOP increase with 43% having a ≥50% increase.ConclusionLateral and prone sleeping positions usually do result in significant elevations of IOP in PD patients. Dependency status did not make a difference. A significantly larger IOP increase was seen in the prone position than in the lateral position. The presence of 3 clinical variables (disk hemorrhage [DH], notches, and BV changes) might increase the chances of developing a large recumbent increase in IOP. These patients and possibly all PD syndrome (PDS) or PD glaucoma (PDG) patients should consider sleeping in a bed that allows a head elevation of 30°.

On the theory of adsorption on graphene-like compounds

Based on a previously proposed model of the electronic spectrum of binary ANB8–N graphene-like compounds (GLC), adsorption theory is constructed, which allows determination of the role of the adatom level position, the adatom–substrate coupling constant, and the gap inherent to GLC in the free state with heteropolar bonds in the formation of the adatom electronic structure. The cases of free-standing and epitaxial GLCs on a metal surface are considered. In the case of free-standing GLCs, analysis shows local states mainly contribute to the adatom occupation number na at large and intermediate adatom–GLC coupling constants; as the coupling constants decrease, the contribution of the GLC valence band increases. The main feature of an epitaxial GLC on metal is the absence of a gap, hence, the contribution of adatom local states to na. Estimations show that changes in the adatom–substrate and GLC–metal coupling constants affect na in almost the same way. In this case, the dependence of na on the GLC gap is not critical from the qualitative viewpoint. Adsorption on the GLC–semiconductor structure is briefly discussed.

Early Postoperative Outcomes of Primary Bariatric Surgery in Patients on Chronic Steroid or Immunosuppressive Therapy.

Previous research suggests that patients on chronic steroids may be at an increased risk of postoperative morbidity after major surgery. We aimed to evaluate the prognostic impact of chronic use of steroid or immunosuppression on 30-day morbidity and mortality rates after primary bariatric surgery. From American College of Surgeons-National Surgical Quality Improvement Program (ACS-NSQIP) database, we identified patients who underwent primary bariatric surgery between 2005 and 2013. Logistic regression was used to determine the prognostic impact of chronic use of steroid or immunosuppression on the 30-day postoperative outcomes. One thousand two hundred seventy seven steroid/immunosuppressant-dependent (SD) and 112,892 non-dependent (ND) patients were analyzed. SD patients had a higher baseline risk profile compared to ND patients. Thirty-day mortality rates for SD and ND patients were 0.55 and 0.11%, respectively (P < 0.001) which corresponds to an adjusted odds ration (OR) of 6.85 (95% confidence interval (CI) 1.95-24.12). SD patients had a higher 30-day major morbidity compared to ND patients (5.01 versus 2.54%; P < 0.001, respectively). After adjustment, this translated into an OR of 2.21 (95% CI 1.29-3.79). Among SD patients, there was no significant difference in 30-day major morbidity after gastric bypass compared to sleeve gastrectomy (OR = 0.36; 95% CI 0.08-1.66). Chronic and active use of steroid or immunosuppressant medications is a strong predictor of 30-day postoperative morbidity and mortality following primary bariatric surgery. Among the steroid/immunosuppressant users, complication rates were similar for gastric bypass and sleeve gastrectomy patients. Further studies are needed to help guide the management or discontinuation of such medications in the perioperative period.

Atypical valuation of monetary and cigarette rewards in substance dependent smokers

ObjectiveSubstance dependent (SD) relative to non-dependent (ND) individuals exhibit an attenuated reward positivity, an electrophysiological signal believed to index sensitivity of anterior cingulate cortex (ACC) to rewards. Here we asked whether this altered neural response reflects a specific devaluation of monetary rewards relative to drug-related rewards by ACC. MethodsWe recorded the reward positivity from SD and ND individuals who currently smoke, following an overnight period of abstinence, while they engaged in two feedback tasks. In a money condition the feedback indicated either a monetary reward or no reward, and in a cigarette condition the feedback indicated either a drug-related reward or no reward. ResultsOverall, cigarette relative to monetary rewards elicited a larger reward positivity. Further, for the subjects who engaged in the money condition first, the reward positivity was smaller for the SD compared to the ND participants, but for the subjects who engaged in the cigarette condition first, the reward positivity was larger for the SD compared to the ND participants. ConclusionsOur results suggest that the initial category of feedback “primed” the response of the ACC to the alternative feedback type on subsequent trials, and that SD and ND individuals responded differently to this priming effect. SignificanceWe propose that for people who misuse addictive substances, the prospect of obtaining drug-related rewards engages the ACC to exert control over extended behaviors.

Memantine reduces alcohol drinking but not relapse in alcohol-dependent rats.

Alcoholism is a chronic relapsing disorder with consequences on health and that requires more effective treatments. Among alternative therapies, the therapeutic potential of the non-competitive N-methyl-D-aspartate receptor antagonist memantine has been suggested. Despite promising results, its efficiency in the treatment of alcoholism remains controversial. Currently, there is no pre-clinical data regarding its effects on the motivation for ethanol in post-dependent (PD) animals exposed to intermittent ethanol vapor, a validated model of alcoholism. Thus, the objectives of this study were to evaluate the effects of acute injections of memantine (0, 12.5, 25 and 50 mg/kg) on operant ethanol self-administration in non-dependent (ND) and PD rats tested either during acute withdrawal or relapse after protracted abstinence. Our results showed that memantine (25 mg/kg) abolished ethanol self-administration in ND rats and reduced by half the one of PD rats during acute withdrawal. While this effect was observed only 6 hours after treatment in ND rats, it was long lasting in PD rats (at least 30 hours after injection). Furthermore, our results indicated that memantine did not modify the breaking point for ethanol. This suggests that memantine probably act by potentiating the pharmacological effect of ethanol but not by reducing motivation for ethanol. Finally, memantine was also ineffective in reducing relapse after protracted abstinence. Altogether, our pre-clinical results highlighted a potential therapeutic use of memantine that may be used as a replacement therapy drug but not as relapse-preventing drug.

FXYD Proteins Reverse Inhibition of the Na+-K+ Pump Mediated by Glutathionylation of Its β1 Subunit

The seven members of the FXYD protein family associate with the Na(+)-K(+) pump and modulate its activity. We investigated whether conserved cysteines in FXYD proteins are susceptible to glutathionylation and whether such reactivity affects Na(+)-K(+) pump function in cardiac myocytes and Xenopus oocytes. Glutathionylation was detected by immunoblotting streptavidin precipitate from biotin-GSH loaded cells or by a GSH antibody. Incubation of myocytes with recombinant FXYD proteins resulted in competitive displacement of native FXYD1. Myocyte and Xenopus oocyte pump currents were measured with whole-cell and two-electrode voltage clamp techniques, respectively. Native FXYD1 in myocytes and FXYD1 expressed in oocytes were susceptible to glutathionylation. Mutagenesis identified the specific cysteine in the cytoplasmic terminal that was reactive. Its reactivity was dependent on flanking basic amino acids. We have reported that Na(+)-K(+) pump β(1) subunit glutathionylation induced by oxidative signals causes pump inhibition in a previous study. In the present study, we found that β(1) subunit glutathionylation and pump inhibition could be reversed by exposing myocytes to exogenous wild-type FXYD3. A cysteine-free FXYD3 derivative had no effect. Similar results were obtained with wild-type and mutant FXYD proteins expressed in oocytes. Glutathionylation of the β(1) subunit was increased in myocardium from FXYD1(-/-) mice. In conclusion, there is a dependence of Na(+)-K(+) pump regulation on reactivity of two specifically identified cysteines on separate components of the multimeric Na(+)-K(+) pump complex. By facilitating deglutathionylation of the β(1) subunit, FXYD proteins reverse oxidative inhibition of the Na(+)-K(+) pump and play a dynamic role in its regulation.

Dépendance physiologique et fonctionnement émotionnel chez les jeunes adultes : affectivité, intensité émotionnelle et alexithymie dans la consommation de substances psychoactives

Objectives The objective of this study is to describe the emotional functioning of individuals addicted to psychoactive substances, and verify that the dependent subjects are more sensitive to emotional dimensions and variables considered as non-dependent subjects. Patients and methods We recruited 268 subjects students. They filled out a protocol, first, a questionnaire assessment measuring dependencies (tobacco, alcohol, cannabis), and a second part consisting of four questionnaires: the Hospital Anxiety Depression (HAD) scale (anxiety and depression), the Émotionalité Positive et Négative (EPN-31) (affectivity), the Affect Intensity Measure (AIM) (affect intensity), and the Toronto Alexithymia Scale (TAS-20) (alexithymia). The 268 subjects were divided into: 69 subjects dependent (D) representing 25.7% of the sample, and 199 non-dependent (ND) subjects, representing 74.3%. It consisted of 224 women and 44 men, mean age was 22.23 years (standard deviation [S.D.]: 5.45, range: 18–56 years). There was no significant difference in gender ( P > 0.05) between groups or in age ( P < 0.05). The scores of anxiety and depression were significantly different between groups. We therefore conducted analysis of covariance (ANCOVA) including the total score of anxiety-depression as a covariate and as dependent variables, scores of emotions, emotional intensity and alexithymia with SPSS 11.5 ®. Results The results show that dependent subjects have scores more important to the HAD than non-dependents, depression has been well regarded as a confounding factor. After controlling for this variable, they are more emotionally responsive, more sensitive to the emotional intensity, and alexithymia more than non-dependent. Activation and the emotional intensity appear to be dispositional variables may play a central role in emotional processing in the dependent subjects, associated with alexithymia. They could be located upstream of the processing of emotion, they would account for the gross apprehension felt by the subject, leading secondarily to the representation of emotion. The proportion of alexithymic subjects is 44.9% in this group of subjects, while only 13.6% among non-dependent subjects. They have greater difficulty in identifying emotions. This supports the idea of the existence of an emotional deficit in individuals addicted to psychoactive substances. This proportion is also larger than that found in general population. Conclusions The alexithymia seems to be a central variable emotional functioning dependent subjects, regardless of its relationship with depression, it could match the emotional processing mode preferred by the subjects dependent. Personality in this study seemed to reflect a vulnerability factor, which alexithymia represents a secondary dimension, even defensive. This could account for a mode of emotional regulation. The limitations of the study and possible openings will be discussed.

Residues Contributing to the Na+-binding Pocket of the SLC24 Na+/Ca2+-K+ Exchanger NCKX2

Na(+)/Ca(2+)-K(+) exchangers (NCKX; gene family SLC24) are plasma membrane Ca(2+) transporters that mediate the extrusion of one Ca(2+) ion and one K(+) ion in exchange for four Na(+) ions. NCKX is modeled to have two sets of five transmembrane segments separated by a large cytosolic loop; within each set of transmembrane segments are regions of internal symmetry termed alpha(1) and alpha(2) repeats. The central residues that are important for Ca(2+) and K(+) liganding and transport have been identified in NCKX2, and they comprise three central acidic residues, Glu(188) in alpha(1) and Asp(548) and Asp(575) in alpha(2), as well as Ser/Thr residues one-helical turn away from these residues. In this study, we have scanned through more than 100 single-residue substitutions of NCKX2 for shifts in Na(+) affinity using a fluorescence assay to monitor changes in free Ca(2+) in HEK293 cells treated with gramicidin to control intracellular Na(+). We have identified 31 residues that, when substituted, result in shifts in Na(+) affinity, either toward higher or lower K(m) values when compared with wild type NCKX2 (K(m) for Na(+) 58 mm). These residues include the central acidic residues Glu(188), Asp(548), and Asp(575), and their neighboring residues in alpha(1) and alpha(2), in addition to a number of newly investigated residues in transmembrane segment 3. Our results relate the identification of residues important for Na(+) transport in this study to those previously identified as important in the counter-transport of Ca(2+) and K(+), lending support to the alternating access model of transmembrane transport.

Kinetic properties of sodium transport pathways in the river lamprey Lampetra fluviatilis erythrocytes

To activate Na+/H+ exchange, intracellular pH (pHi) of erythrocytes of the river lamprey Lampetra fluviatilis were changed from 6 to 8 using nigericin. The Na+/H+ exchanger activity was estimated from the values of amiloride-sensitive components of Na+ (22Na) inflow or of H+ outflow from erythrocytes. Kinetic parameters of the carrier functioning were determined by using Hill equation. Dependence of Na+ and H+ transport on pHi value is described by hyperbolic function with the Hill coefficient value (n) close to 1. Maximal rate of ion transport was within the limits of 9-10 mmol/l cells/min, and the H+ concentration producing the exchanger 50% activation amounted to 0.6-1.0 microM. Stimulation of H+ outcome from acidified erythrocytes (pHi 5.9) with increase of H+ concentration in the incubation medium is described by Hill equation with n value of 1.6. Concentration of Na+: for the semimaximal stimulation of H+ outcome amounted to 19 mM. The obtained results indicate the presence in lamprey erythrocytes of only one binding site for H+ from the cytoplasm side and the presence of positive cooperativity in Na+ binding from the extracellular side of the Na+/H+ exchanger. Its efflux from cells in the Na+ -free medium did not change at a 10-fold increase of H+ concentration in the incubation medium. The presented data indicate differences of kinetic properties of the lamprey erythrocyte Na+/H+ exchanger and of this carrier isoforms in mammalian cells. In intact erythrocytes the dependence of the amiloride-sensitive Na+ inflow on its concentration in the medium is described by Hill equation with n 1.5. The Na+ concentration producing the 50% transport activation amounted to 39 mM and was essentially higher as compared with that in acidified erythrocytes. These data confirm the concept of the presence of two amiloride-sensitive pathways of Na+ transport in lamprey erythrocytes.

Ferrying Fuel to the Sodium Pump

Jung et al . investigated enhancement of Na + ,K + -ATPase (adenosine triphosphatase) activity by the actin-binding protein cofilin and discovered a novel regulatory mechanism in which cofilin recruits the glycolytic enzyme triose-phosphate isomerase (TPI) to provide a ready supply of ATP. Na + ,K + -ATPase plays a crucial role in cell volume regulation and electrical signaling by using energy from the hydrolysis of ATP, preferentially derived from glycolysis, to maintain Na + and K + gradients across the cell membrane. Cofilin, which, when dephosphorylated, promotes actin filament turnover and thereby plays a role in cellular processes that depend on actin dynamics, interacts with Na + ,K + -ATPase and enhances its activity. Jung et al . used a yeast two-hybrid assay to screen a rat skeletal muscle cDNA library and discovered that cofilin interacted with TPI. The association of cofilin, TPI, and Na + ,K + -ATPase was confirmed in vivo both by immunofluorescence and by Western analysis of immunoprecipitates of HeLa cells transfected with labeled cofilin and labeled TPI. Pharmacological analysis indicated that activation of Rho signaling pathways resulted in translocation of cofilin and TPI to the cell membrane and increased association with Na + ,K + -ATPase. Activating Rho or overexpressing cofilin increased Na + ,K + -ATPase activity, as assessed by ouabain-sensitive 86 Rb + uptake. However, inhibiting the Rho pathway, or overexpressing cofilin-S3A, a mutant form that could not be phosphorylated, attenuated Na + ,K + -ATPase activity. Pharmacological analysis indicated that Rho pathway activation led to decreased [Na] i and confirmed the dependence of Na + ,K + -ATPase on glycolytic supplies of ATP, rather than ATP derived from oxidative phosphorylation. The data suggest a role for phosphorylated cofilin, and for Rho, in regulation of the Na + ,K + -ATPase. J. Jung, T. Yoon, E. C. Choi, K. Lee, Interaction of cofilin with triose-phosphate isomerase contributes glycolytic fuel for Na + ,K + -ATPase via Rho-mediated signaling pathway. J. Biol. Chem. 277 , 48931-48947 (2002). [Abstract] [Full Text]

Diet deficient in alpha-linolenic acid alters fatty acid composition and enzymatic properties of Na +, K +-ATPase isoenzymes of brain membranes in the adult rat

The effects of dietary (n-6)/(n-3) polyunsaturated fatty acid balance on fatty acid composition, ouabain inhibition, and Na + dependence of Na +, K +-ATPase isoenzymes of whole brain membranes were studied in 60-day-old rats fed over two generations a diet either devoid of α-linolenic acid [18:3(n-3)] (sunflower oil diet) or rich in 18:3(n-3) (soybean oil diet). In the brain membranes, the sunflower oil diet led to a dramatic decrease in docosahexaenoic acid [22:6(n-3)] membrane content. The activities of Na +, K +-ATPase isoenzymes were discriminated on the basis of their differential affinities for ouabain and their sensitivity to sodium concentration. The ouabain titration curve of Na +, K +-ATPase activity displayed three inhibitory processes with markedly different affinity [i.e., low (α1), high (α2), and very high (α3)] for brain membranes of rats fed the sunflower oil diet, whereas the brain membranes of rats fed the soybean oil diet exhibited only two inhibitory processes, low (α1) and high (α2′ = α2 + α3). Regardless of the diet, on the basis of the Na + dependence of Na +, K +-ATPase activity, three isoenzymes were found: α1 form displaying an affinity 1.5- to 2-fold higher that of than α2 and 3-fold higher that of α3. In rats fed the sunflower oil diet, α2 isoenzyme exhibited higher affinity for sodium (Ka = 8.8 mmol/L) than that of rats fed the soybean oil diet (Ka = 11.7 mmol/L). These results suggest that the membrane lipid environment modulates the functional properties of Na +, K +-ATPase isoenzymes of high ouabain affinity (α2).

Weakening of ion-channel interactions of Na+ and Li+ in acetylcholine-receptor channels of frog skeletal muscle with an increase in agonist concentration.

The possibility that increases in agonist concentration beyond threshold levels may force changes in the character of high-conductance open states of skeletal muscle nicotinic acetylcholine receptor channels (nAChR) was examined by seeing whether differences in several critical ionic properties of nAChR currents could be detected with changes in agonist level. Single- and bi-ionic whole-cell currents of Na+ and Li+ in voltage-clamped frog (Rana pipiens) muscle fibers were measured during local superfusion of endplates with carbamylcholine (carb) at concentrations of 54 microm (low-carb) and 270 microM (high-carb). Three ionic properties that would be affected by changes in the open-state configuration of channel subunits were tested. First, ion-saturation characteristics. Peak Na+ and Li+ currents in low-carb trials showed sublinear dependence on ion concentrations from 0 to 60 mM with Km values of 78 (Na+) and 49 (Li+) mM and a power function slope of 0. 75 on double-log plot. In contrast, the concentration dependence of Na+ and Li+ currents in high-carb tests was linear through the origin with a power function slope of 1.02. Second, Na+/Li+ selectivity. The ratio of peak Na+ and Li+ currents in low-carb tests varied from 1.86 to 2.28 for ion concentrations of from 20 to 60 mM [mean = 2.02 +/- 0.06 (SEM)] whereas the ratio for high-carb trials ranged from only 1.29 to 1.52 [mean = 1.42 +/- 0.40 (SEM)]. Third, competitive interactions of Na+ and Li+ currents. Equimolar mixtures of Na+ and Li+ in low-carb tests produced bi-ionic inward currents which were never larger than the single-ion Na+ current alone, but bi-ionic currents at the high-carb level were always greater than the single-ion Na+ current, approximating the sum of the single-ion Na+ and Li+ currents in most cases. The results are consistent with a decrease in ion-channel binding at the high-carb level and support the possibility of agonist-induced changes in the high-conductance open-state configuration of nAChR subunits which result in a weakening of constraints on cation movements through the channel.

Na(+)-D-glucose cotransport by intestinal BBMVs of the Antarctic fish Trematomus bernacchii.

Intestinal nutrient absorption in fish adapted to low temperature was investigated by isolating, with a Mg(2+)-precipitation procedure, brush-border membrane vesicles (BBMVs) from intestines of the Antarctic teleost Trematomus bernacchii. In particular, D-glucose transport was analyzed by measuring both 1) fluorescence changes of the electrical potential-sensitive dye 3,3'-diethylthiadicarbocyanine iodide [DiS-C2(5)] and 2) intravesicular uptake of D-[14C]glucose. Results demonstrated that transport of D-glucose across intestinal BBMs of the Antarctic fish is stimulated by the presence of a transmembrane Na+ gradient (out > in) and was specifically inhibited by phloridzin. Furthermore, Na(+)-dependent D-glucose uptake was strongly enhanced by the presence of an electrical potential (inside-negative) across the membrane. There was a marked difference in temperature dependence of Na(+)-sugar cotransport between the Antarctic fish and a temperate fish, such as the European yellow eel., Na(+)-dependent D-glucose uptake in T. bernacchii intestinal BBMV reached its maximal rate at -2-0 degree C (close to fish living temperature) and was exponentially inactivated by incubation at higher temperatures. Kinetic analysis of D-glucose influx indicated the presence of a single Na(+)-dependent carrier process (apparent maximal carrier-mediated influx = 0.233 +/- 0.009 nmol.mg protein-1.min-1; apparent half-saturation constant for carrier-mediated influx = 0.157 +/- 0.026 mmol/l) and a nonsaturable transfer component (apparent diffusional permeability of membrane to the sugar = 0.233 +/- 0.016 microliter.mg protein-1.min-1). The Na(+)-dependent carrier-mediated mechanism was specific for sugars, since it was partially inhibited by the presence in the extravesicular medium of other monosaccharides, but not by ascorbic acid or amino acids of different types. These data suggest that in the intestine of Antarctic fish luminal D-glucose transport takes place by a specific Na(+)-dependent electrogenic secondary active transport working well at subzero temperatures.

Dependence of Na+ and Cl− transport in the neonatal pig intestine on delivery and gestational age

Dependence of Na+ and Cl− transport in the neonatal pig intestine on delivery and gestational age

Demonstration of temperature dependence of Na(+)-K+ pump activity of human blood cells.

In our physiology laboratory course we introduced several simple but instructive experiments in which medical students make observations on their own blood cells. In this experiment, students measured and discussed the effect of different temperatures on Na+ and K+ distribution between blood cells and plasma. In venous blood of 35 female and 64 male students, plasma (extracellular) [Na+] and [K+] were measured with ion-selective electrodes immediately after blood sampling and successively four times in intervals of 1 h in three samples stored at 1, 20, and 37 degrees C. At 1 degree C, plasma [K+] increased significantly and nearly linearly with cooling time of the blood, whereas plasma [Na+] decreased. In contrast, at 37 degrees C plasma K+ levels significantly decreased in the first 2 h and then stabilized at new levels clearly below baselines. At 1 degree C blood cells had a greater K+ loss in women than in men, whereas at 37 degrees C the K+ loss was significantly less pronounced in women. Plasma Na+ did not significantly change at 37 degrees C. This remarkably reproducible experiment demonstrates the existence of active Na(+)-K+ transport in human blood cells by showing medical students, with their own blood, that the basal chemical processes of such pumps are inhibited at a temperature of 1 degree C and stimulated when blood temperature is slightly higher than the usual body temperature.